Practically all existing office computer systems, such as that depicted in FIG. 1, comprise a number of workstation computers 13 connected to some local area network (LAN) 11. One or more dedicated computers act as a file server 10. These file servers provide access to attached storage devices, such as disk drives 14, which contain the shared data files. These data files are retrieved or updated by the file server in accordance with requests transmitted by workstation computers over the local area network. The local area network also carries communications between workstation computers.
The local area network 11 is essentially a shared data transmission medium. As such, the capacity of the medium is shared between the workstation computers 13 attached to it. In order to effect higher performance of the local area network, LAN switches 12 are used. These are also known as filtering bridges. In this type of arrangement the local area network is split into several independent segments 11A and 11B which are interconnected with a LAN switch. The LAN switch is programmed with, or automatically discovers, data regarding the connection arrangement of workstation computers and corresponding segments. Because of this data, LAN switch is able to route traffic only to relevant segments of the LAN, thus eliminating unnecessary traffic on other segments of the local area network. For large local area networks, a substantial number of segments can be created to be interconnected by multiple LAN switches.
Algorithms and systems for remote access to shared files are well known in the conventional technology. Such systems and techniques are described in numerous publications, such as Managing NFS and NIS by Hal Stem, published by O'Reilly & Associates, Inc., Jun. 1991).
Conventional arrangements allow aggregate LAN capabilities in excess of the normal capacity of the LAN physical medium. While this approach achieves aggregate LAN capacities far in excess of that of LAN physical media, the capacity of the segment 11B between the file server 10 and the LAN switch 12 remains limited. When a substantial number of workstation computers 13 request access to shared data files, via their respective segments 11A and LAN switch 12, the segment 11B can quickly become overloaded.
To avoid the problem of overload in segment 11B several approaches have been used in conventional systems. The first approach is to make use of high-speed interconnection technologies, such as the 100-Mbps Ethernet. However, this approach is severely limited by the difficulty inherent to processing and transmitting radio-frequency signals. These difficulties severely limit the maximum usable capacity of the file server. Use of the single high-speed data path renders the overall system very fragile since any failure in the high-speed data path is likely to disable large parts of the entire local area network.
A second approach is described in U.S. Pat. No. 5,548,724 to Akizawa et al. (1994). The system disclosed therein includes a plurality of file servers running very complicated and elaborate load-balancing software. The complexity of required software (as well as its high cost) and the difficulty of administration of numerous separate file servers render this approach impractical. Further, such systems also require extensive modification of software running on workstation computers to support switching to alternative file servers in case of a failure in a particular file server or in a portion of the system linking the workstation computers to file servers. All of these considerations render this approach far too expensive for most applications.
In a third approach a packet router is used instead of the LAN switch 12, so as to separate the logical network into a plurality of different sub-networks. A file server is attached to more than one sub-network, so the traffic from different sub-networks will reach the file server through different physical links. This approach does not scale (upwards in performance) well and requires use of an expensive router. This system also requires administrative changes in configurations of workstation computers (to be performed by skilled personnel) every time a workstation computer is moved from one sub-network to another. Local area networks built using this approach are vulnerable to failures in both the packet router and the file server.
A number of examples of additional approaches to improvement of performance of local area networks are found in the following documents: U.S. Pat. No. 5,485,627 to Hillis (1996); U.S. Pat. No. 5,243,704 to Baty et. al. (1993); U.S. Pat. No. 5,475,856 to Kogge (1995); U.S. Pat. No. 4,942,517 to Cok (1990); U.S. Pat. No. 5,355,453 to Row et. al. (1994); U.S. Pat. No. 5,163,131 to Row et al. (1992); and U.S. Pat. No. 4,577,272 to ballew et. al. (1996). All of these references disclose methods for improving the performance of file servers by using multiple processing units working in parallel. However, each system fails to address the issue of the capacity of the link between the file server and the LAN switch. These examples also fail to improve reliability of the whole LAN since they are primarily directed only to the reliability of single components within the local area network.